linuxthreads/sysdeps/i386/pt-machine.h

   1 /* Machine-dependent pthreads configuration and inline functions.
   2    i386 version.
   3    Copyright (C) 1996, 1997, 1998 Free Software Foundation, Inc.
   4    This file is part of the GNU C Library.
   5    Contributed by Richard Henderson <rth@tamu.edu>.
   6
   7    The GNU C Library is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU Library General Public License as
   9    published by the Free Software Foundation; either version 2 of the
  10    License, or (at your option) any later version.
  11
  12    The GNU C Library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    Library General Public License for more details.
  16
  17    You should have received a copy of the GNU Library General Public
  18    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  19    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  20    Boston, MA 02111-1307, USA.  */
  21
  22 #ifndef PT_EI
  23 # define PT_EI extern inline
  24 #endif
  25
  26 /* Spinlock implementation; required.  */
  27 PT_EI int
  28 testandset (int *spinlock)
  29 {
  30   int ret;
  31
  32   __asm__ __volatile__(
  33        "xchgl %0, %1"
  34        : "=r"(ret), "=m"(*spinlock)
  35        : "0"(1), "m"(*spinlock)
  36        : "memory");
  37
  38   return ret;
  39 }
  40
  41
  42 /* Get some notion of the current stack.  Need not be exactly the top
  43    of the stack, just something somewhere in the current frame.  */
  44 #define CURRENT_STACK_FRAME  stack_pointer
  45 register char * stack_pointer __asm__ ("%esp");
  46
  47
  48 /* Compare-and-swap for semaphores.
  49    Available on the 486 and above, but not on the 386.
  50    We test dynamically whether it's available or not. */
  51
  52 #define HAS_COMPARE_AND_SWAP
  53 #define TEST_FOR_COMPARE_AND_SWAP
  54
  55 PT_EI int
  56 __compare_and_swap (long int *p, long int oldval, long int newval)
  57 {
  58   char ret;
  59   long int readval;
  60
  61   __asm__ __volatile__ ("lock; cmpxchgl %3, %1; sete %0"
  62                         : "=q" (ret), "=m" (*p), "=a" (readval)
  63                         : "r" (newval), "m" (*p), "a" (oldval));
  64   return ret;
  65 }
  66
  67
  68 extern inline int
  69 get_eflags (void)
  70 {
  71   int res;
  72   __asm__ __volatile__ ("pushfl; popl %0" : "=r" (res) : );
  73   return res;
  74 }
  75
  76
  77 extern inline void
  78 set_eflags (int newflags)
  79 {
  80   __asm__ __volatile__ ("pushl %0; popfl" : : "r" (newflags) : "cc");
  81 }
  82
  83
  84 PT_EI int
  85 compare_and_swap_is_available (void)
  86 {
  87   int oldflags = get_eflags ();
  88   int changed;
  89   /* Flip AC bit in EFLAGS.  */
  90   set_eflags (oldflags ^ 0x40000);
  91   /* See if bit changed.  */
  92   changed = (get_eflags () ^ oldflags) & 0x40000;
  93   /* Restore EFLAGS.  */
  94   set_eflags (oldflags);
  95   /* If the AC flag did not change, it's a 386 and it lacks cmpxchg.
  96      Otherwise, it's a 486 or above and it has cmpxchg.  */
  97   return changed != 0;
  98 }